The use of roofing membranes as a waterproofing material on buildings is well known. The typical type of roofing membrane consists of a base sheet of a sheet-like material such as, for example, paper, felt, fabric, synthetic polymer film, woven or non-woven fabric, glass fibers, or metal foil with a bitumen layer coated on both faces of the base sheet. Mineral granules or powder such as fine gravel, sand, or talcum are embedded in the surface of the bitumen layer in order to suppress the stickiness of the bitumen and also to protect the exposed bitumen layer from ultraviolet light after the bituminous roofing membrane is applied on site. The bottom of the membrane is covered with a layer of asphalt which is embedded with a back surfacing material such as sand to prevent the membrane from sticking to another membrane material during shipping and handling.
The above-described conventional roofing membrane is not without problems, however. The asphalt impregnated product has limited elongation properties which make it tend to buckle or crack upon thermal expansion and contraction. Additionally, the resulting roof membrane has only a minimal aesthetic value. Also, because the granules are embedded in the surface layer, gaps exist between the granules such that complete protection of the bitumen (or asphalt) from ultraviolet light may not be achieved. Consequently, the conventional roofing material suffers from commercial limitations.
Detecting that there was both a need and a demand in the building industry for an improved roofing membrane product, Applicants devised a novel laminate material which makes an economical yet excellent roofing material.